1. Field of the Invention
This invention relates to a tape loading device, and is best applicable to a cassette tape recording and/or reproducing apparatus for a digital VTR, for example.
2. Description of the Prior Art
For instance, in the disclosure of U.S. Pat. No. 4,652,946, a big capstan incorporated in a tape loading device for a digital VTR is brought into contact with the back surface (not the front surface which is coated with magnetic powder) of a magnetic tape so as to protect the coated front surface.
In such tape loading device, the big captan is arranged below a compartment wherein a tape cassette is horizontally withdrawn into the VTR and horizontally mounted, from above, on a pair of reel hases. Further, the capstan is inserted, from below and together with a plurality of tape loading means, into a space formed between the tape cassette and a portion of the tape which has been stretched within an opening that is provided on a front side of the tape cassette.
While the tape is drawn from the tape cassette by the plurality of tape loading means after the tape cassette is mounted, the tape is wrapped around the capstan at a predetermined contact angle by a pair of tape guides which are moved in a reverse direction for the tape being drawn by the tape loading means, and when the record mode, the playback mode or the like is established, the tape is driven by friction caused between the capstan and the back surface of the tape.
However, in such tape loading device, the tape loading means and the tape guides are moved in the opposite direction of each other, so that the tape is excessively stretched between the tape loading means and the tape guides, and often receives damages.
If the back tension of the tape is reduced to prevent the tape from such damage, the tape is apt to slip out of the tape loading means, so that it becomes difficult to load the tape at high speed.
Moreover, there is naturally a limit to the area and height of the opening of the tape cassette, into which the captan, the plurality of tape loading means, and also the pair of tape guides are inserted at a time of tape loading, so that it is difficult to make the diameter and the length of the capstan large. The small diameter of the capstan prevents the tape from running at high speed so as to shorten access time, and the small length of the capstan prevents the tape from running stably. Further, the compartment above the capstan interferes with the maintenance of the capstan.
In the meantime, in the conventional tape loading device for VTRs, a tape-tension adjusting device 231 shown in FIG. 11 is widely used, for example, as disclosed in Japanese Laid Open Utility Model Registration No. 56-152958. In FIG. 11, a supply reel base 220 is rotatably supported by a chassis of the VTR (not shown), and around the supply reel base 220, a band brake 221 is wrapped. An arm 225 is rotatable on a shaft 223 which projects from the chassis, and has a tape guide 224 at the distal end thereof and a projection at the proximal end thereof. One end of the band brake 221 is fixed to the chassis, and the other end is connected, through a pin 226, to the free end of the projection of the arm 225. A magnetic tape T unwound from a reel that is mounted on the reel base 220 is wrapped around the tapeguide 224 and fed to a rotary head drum (not shown).
To give back tension to the tape T, a tension spring 228 is stretched between an intermediate position 225a of the arm length and an spring stop 227a which is provided in a worm wheel 227 that is rotatably supported by the chassis and meshed with a worm 230. The torque of a motor 229 is imparted to the worm 230 through a belt 229b. Thus, the tape-tension adjusting device 231 comprises the band brake 221, the arm 225 and the tension spring 228, and the tape tension is detected through the tape guide 224 of the arm 225.
If the tape tension is too large, the motor 229a is driven to rotate the worm wheel 227 counterclockwise in FIG. 11, so that the tension of the spring 228 is reduced so as to rotate the arm 225 counterclockwise. As a result, the braking force of the band brake 221, which acts on the supply reel base 220, is reduced. On the contrary, if the tape tension is too small, the worm wheel 227 is rotated clockwise in FIG. 11, so that the tension of the spring 228 is increased so as to rotate the arm 225 clockwise. As a result, the braking force is increased. That is, the back tension of the tape T is adjusted due to rotation of the worm wheel 227, so that the tape T can be made to stably run.
However, the tape-tension adjusting device 231 described above has no means to detect the angle of rotation of the arm 225 in order to adjust the tension of the spring 228, so that as shown in FIG. 12, the tension of the tape T remarkably increases for a transition period, for example, while the stop mode is changed over to the play back mode. Thus, the tape T is often damaged.